The measurement sensitivity of microwave surface resistance, Rs, of high temperature superconducting (HTS) thin films using half-wavelength microstrip resonator with copper and HTS ground plane is analyzed for fundamental and higher order modes of the resonator. The estimated sensitivity of Rs-measurement is at least an order of magnitude greater at fundamental resonant frequency compared to when measured using higher order harmonic modes.

We fabricated ramp-edge junctions with barriers by modifying surface and integrating ground-planes. The fabricated junctions had current-voltage characteristics consistent with the resistive shunted-junction model. We also obtained a 1-sigma spread in the critical current of 7.9% for 100 junctions at 4.2 K. The ground-plane reduced the sheet inductance of a stripline by a factor of 3. The quality of the ground-plane was improved by using an anneal in oxygen atmosphere after fabrication. The sheet inductance of a counter-electrode with a ground-plane was 1.0 pH per square at 4.2 K.

This paper introduces a probabilistic modeling of alarm observation delay, and shows a novel method of model-based diagnosis for time series observation. First, a fault model is defined by associating an event tree rooted by each fault hypothesis with probabilistic variables representing temporal delay. The most probable hypothesis is obtained by selecting one whose Akaike information criterion (AIC) is minimal. It is proved by simulation that the AIC-based hypothesis selection achieves a high precision in diagnosis.

Pulse tube cryocoolers receive considerable attention due to their intrinsically higher durability and lower vibrations than other regenerative coolers such as Gifford-McMahon or Stirling cycle coolers. This paper describes basic function and classification of the pulse tube cryocoolers from the viewpoint of electronic applications.

A method of learning for multi-layer artificial neural networks is proposed. The learning model is designed to provide an effective means of escape from the Backpropagation local minima. The system is shown to escape from the Backpropagation local minima and be of much faster convergence than simulated annealing techniques by simulations on the exclusive-or problem and the Arabic numerals recognition problem.

A highly stable oven-controlled crystal oscillator (OCXO) with low phase-noise characteristics has been developed using a dual-mode SC-cut quartz crystal oscillator. The OCXO uses a conventional oven-control system for coarse compensation and a digital-correction system, which uses B-mode signal in an SC-cut resonator as a temperature sensor, for fine compensation. Combining these two forms of compensation greatly improves the stability of the C-mode frequency without requiring a double-oven system. The experimental results indicated that the frequency stability of the proposed OCXO, including the frequency-temperature hysteresis, is ten times better than that of a conventional, free-running OCXO. The results also indicated that the proposed OCXO has good frequency retraceability and low phase-noise characteristics.

Breakthroughs in crystal growth and conductivity control of nitride semiconductors during last two decades have led to such developments as high-brightness blue and green light-emitting diodes and long-lived violet laser diodes and so on. All of these nitride-based devices are robust and the most environmentally-friendly ones available. They enable us to save tremendous amount of energy and will be key devices in advanced information technology. Further progress in the area of crystal growth and device engineering will open up new frontier devices based on nitride semiconductors. In this paper, the evolution of nitride-based light-emitting devices is reviewed and the key issues, which must be addressed for nitrides to be fully developed, are discussed.

A novel sensor system of denture base type was developed for simultaneous monitoring of salivary pH and tissue temperature in the oral cavity. Fundamental components of the monitoring system, sensor devices and sensor configuration are showed in this paper. The sensor units consist of IrO2 electrode and thermistor circuit implanted in the denture base that is tightly fixed in the oral cavity. The signals are transmitted by PFM-FM telemeter system that can be used for health care of the aged people without restraint of their daily behavior while at work, sleeping and even at exercise. Some of results concerning the basic characteristics of the sensor system and continuously monitored physiological data were obtained from the preliminary experiments. Availability of the whole system and monitoring method was discussed.

A GaInNAs alloy on GaAs substrate has been very promising for long-wavelength vertical-cavity surface-emitting lasers (VCSELs) as an active layer. In spite of many groups reported the excellent temperature characteristics of the threshold current of the GaInNAs/GaAs edge-emitting lasers, discussions of the temperature dependence of the lasing characteristics except threshold current is few. In this paper, temperature characteristics of GaInNAs lasers grown by chemical beam epitaxy (CBE) emitting at λ=1.27 µm and λ=1.30 µm were investigated in detail. The characteristic temperature (T0) ranging from 10 to 80 varies from 60 to 130 K and decreased with decreasing cavity length for shorter cavity (< 400 µm) devices. On the other hand, longer cavity (< 400 µm) devices show that the cavity length does not affect so much to T0. The internal losses did not increase with increasing temperature. On the other hand, internal quantum efficiencies decreased with increasing temperature. It is considered that non-radiative recombination center with large temperature dependence may influence the decrease of the internal quantum efficiency due to the insufficient crystal quality of GaInNAs layer. The transparency current densities were unchanged for all temperature range, however, the gain constants decreased with increasing temperature. Thus, the decrease of the gain constant is considered to be due to decreasing of gain. Unchanged both transparency current density and internal loss may also express that these temperature characteristics were not induced by carrier overflow but be done by decreasing of the gain. From the results, it is considered that the temperature dependence of the gain originated from the Fermi-Dirac distribution of carriers was dominant for the temperature characteristics of GaInNAs/GaAs lasers. Due to the temperature dependence on the gain, the T0 decreases with increasing mirror loss.

A numerically efficient analysis method, combining closed-form Green's functions with the method of moments (MoM) of the mixed potential integral equation (MPIE) approach, is considered for the electromagnetic coupling problem through an aperture into a parallel plate waveguide (PPW), as a complementary problem to the microstrip patch structure problem, and then applied to the electromagnetic pulse (EMP) penetration problem. Some discussion on the advantages of the present method is also presented from the perspective of computational electromagnetics.

This study is intended to realize an in-situ gas sensor based upon the principle of millimeter/submillimeter wave spectroscopy. In-situ gas sensor will be attractive because of gas selectivity, multiple parametric measurement such as gas temperature, pressure and density, and of the in-situ measurement capability. One of the major technical problem to be solved is to develop an instrument accurate enough to discern the spectrum change due to the variation of parameters such as temperature. In this paper a proposed gas absorption measurement system is investigated, which schematically consists of Fabry-Perot type gas cell for effective long path length, and vector signal processing to reject leak signal coupled between resonator input and output ports so as to achieve precise absorption measurement. Also included is an parametric study of oxygen absorption characteristics, which is served as the predicted value in the evaluation of the instrument. The experiment at 60 GHz and 120 GHz bands using oxygen demonstrates the effectiveness of the current system configuration.

Spatiotemporal chaos in a multidomain regime in a Gunn-effect device is numerically investigated as an example of collective domain oscillations under global constraints. The dynamics of carrier densities are computed using a set of model partial differential equations. Numerical results reveal some distinctive and chaotic clustering features caused by the global coupling and boundary effects. The chaotic regime is then characterized in terms of a Lyapunov spectrum and Lyapunov dimension, the latter increasing with the size of the system.

We fabricated 50-nm-gate InAlAs/InGaAs high electron mobility transistors (HEMTs) lattice-matched to InP substrates by using a conventional process under low temperatures, below 300C, to prevent fluorine contamination and suppress possible diffusion of the Si-δ-doped sheet in the electron-supply layer, and measured the DC and RF performance of the transistors. The DC measurement showed that the maximum transconductance gm of a 50-nm-gate HEMT is about 0.91 S/mm. The cutoff frequency fT of our 50-nm-gate HEMT is 362 GHz, which is much higher than the values reported for previous 50-nm-gate lattice-matched HEMTs. The excellent RF performance of our HEMTs results from a shortening of the lateral extended range of charge control by the drain field, and this may have been achieved because the low-temperature fabrication process suppressed degradation of epitaxial structure.

The temperature compensation technique of InGaP/GaAs power heterojunction bipolar transistor (HBT) with novel bias circuit using Schottky diodes has been developed. The variation in the quiescent current to the temperature is less than 30% from -30C to 90C by this technique, where that is about 125% by the conventional bias circuit. The RF performance of the power HBT MMIC with novel bias circuit shows flat temperature characteristics enough to be used for power application of wireless communications.

Providing results of a series of link-level simulations for a class of spatial and temporal equalizer (S/T-equalizer) is the primary objective of this letter, which is supplemental to this letter's companion article. The S/T-equalizers discussed in this letter have a configuration that can be expressed as the cascaded connection of adaptive array antenna and maximum likelihood sequence estimator (MLSE): each of the adaptive array antenna elements has a fractionally spaced tapped delay line (FTDL), and the MLSE has taps covering a portion of the channel delay profile. Both the desired and interference signals suffer from severe inter-symbol interference (ISI). A major difference of this article from its companion letter is that account is taken of the presence of co-channel interference (CCI). Bit error rate (BER) performance of the S/T-equalizer is presented as a result of the link-level simulations that use field measurement data.

This letter shows the results of a series of link level simulations conducted to evaluate the performances of spatial and temporal equalizers (S/T-equalizers) using field measurement data. The configuration of the spatial and temporal equalizer discussed in this letter can be expressed as a cascade of an adaptive array antenna and maximum likelihood sequence estimator (MLSE): each of the adaptive array antenna elements has a fractionally spaced tapped delay line (FTDL), and the MLSE has taps covering a portion of channel delay profile. Bit error rate (BER) performances of the S/T-equalizers are presented, and performance sensitivity to symbol timing offset is investigated.

An important goal in communication theory is to construct good minimum squared Euclidean distance (MSED) codes for transmission over additive white Gaussian noise (AWGN) channels. In this paper, a new construction method for the M-ary phase-shift-keyed (M-PSK) codes over the ring structure ZM, the ring of integers modulo M, with a good minimum Euclidean distance, is proposed. The proposed codes are linear when multiple coset leaders are considered. The characteristics and performance levels of the newly constructed codes are analyzed for code length up to n 8. It is found that the proposed codes compare favorably with Piret's codes and Graeffe's method codes on Gaussian channels in terms of decoding complexity, coding gain, and error performance.

Using the chirped grating with temperature control, we demonstrated the adaptive dispersion compensation at 40 Gbit/s RZ transmission. The simple monitoring of the 40 GHz frequency component enables us to automatic control of the adaptive dispersion compensator.

Using the chirped grating with temperature control, we demonstrated the adaptive dispersion compensation at 40 Gbit/s RZ transmission. The simple monitoring of the 40 GHz frequency component enables us to automatic control of the adaptive dispersion compensator.

We have measured the temperature dependence of the gain characteristics in 1.3-µm AlGaInAs/InP strained multiple-quantum-well (MQW) semiconductor lasers using Hakki-Paoli method. By measuring the temperature dependences of the peak gain value and the gain peak wavelength, we evaluated the temperature dependences of the threshold current and the oscillation wavelength, respectively. The small temperature dependence of the threshold current in AlGaInAs/InP lasers is caused by the small temperature dependence of the transparency current density, which is represented by the characteristic temperature TJtr of 116 K. In AlGaInAs/InP high T0 lasers, the temperature dependence of the oscillation wavelength is slightly larger than that in GaInAsP/InP lasers because of the larger temperature dependence of bandgap wavelength 0.55 nm/K.